This function enables you to call PHP database functions that are not
natively included in CodeIgniter, in a platform independent manner. For
example, let’s say you want to call the mysql_get_client_info()
function, which is not natively supported by CodeIgniter. You could
do so like this:

$this->db->call_function('get_client_info');

You must supply the name of the function, without the mysql_
prefix, in the first parameter. The prefix is added automatically based
on which database driver is currently being used. This permits you to
run the same function on different database platforms. Obviously not all
function calls are identical between platforms, so there are limits to
how useful this function can be in terms of portability.

Any parameters needed by the function you are calling will be added to
the second parameter.

$this->db->call_function('some_function',$param1,$param2,etc..);

Often, you will either need to supply a database connection ID or a
database result ID. The connection ID can be accessed using:

$this->db->conn_id;

The result ID can be accessed from within your result object, like this: